1. Field
This invention relates to fluid transfer by means of flexible tube displacement pumps. It is particularly directed to an improved positive displacement peristaltic pump, especially useful for medical applications.
2. State of the Art
Positive displacement pumps of various types are well known. Among such devices is a category known as xe2x80x9cflexible tube pumps.xe2x80x9d Such pumps rely upon one or more traveling pressure elements, typically rollers or shoes, pressing against a flexible tube to displace its fluid contents. The traveling elements are carried by a rotor which is powered by an external transmission.
Flexible tube, positive displacement peristaltic pumps have been utilized for low volume fluid transport. In a typical construction, the pressure rollers of such pumps are mounted to revolve within a pump housing at the distal ends of rotor arms. The rollers are mounted on axes transverse the plane on which they revolve, and press against a flexible tube, thereby urging fluid in the tube to move in the direction of roller travel. Positive displacement pumps typically run at low speeds. Accordingly, the rollers are not directly powered; rather, the rotor arms are powered by a drive mechanism external the pump housing. The drive mechanism incorporates a significant gear reduction or a mechanically equivalent speed reducing arrangement.
A positive displacement pump is typically primed by connecting its inlet to a fluid supply, and then running the pump to displace any entrapped air. This process takes time, which is often inconvenient, and in some medical applications, may be life threatening.
The fluid transfer rate of a positive displacement pump is proportional to the speed of rotation of the rotor carrying the traveling pressure elements. Various mechanisms have been utilized to detect this speed. If the pump is operated in pulse mode; i.e., with the pump operating during spaced intervals, the number of rotations during each pulse is of specific importance. Mechanical counters are generally useful for this purpose, but have certain disadvantages. They are irritatingly noisy in medical applications, and they introduce some frictional resistence, which can be problematic in low energy pump applications, generally.
This invention comprises a positive displacement peristaltic pump which incorporates a gear reduction system, or the equivalent, within the pump housing. Moreover, the pressure roller (or rollers) within the housing is driven, and thereby constitutes an element of the reduction system. This arrangement reduces the parts count, cost and space requirements of the pump assembly.
Practical constructions combine one or more eccentric gears from a planetary gear system with a roller arranged to press against a peristaltic tubing, thereby causing pumping action to occur. This arrangement combines eccentric gear reduction and pumping into a single compact cassette, thereby reducing part count and cost. The tubing-to-roller junction also contributes to gear reduction, which increases torque within the system.
The overall gear reduction of the assembly may be divided between components positioned within and outside the housing, depending upon the requirements of a particular application. In any case, incorporating the pressure rollers of the system as a portion of the reduction system constitutes a significant improvement. While pump assemblies constructed in accordance with this invention offer advantages for many applications, one embodiment of particular interest currently is structured as an ambulatory infusion pump for pain management. This structure can readily be adapted to other medical applications requiring the administration of medicaments at low dosage rates on a continuous (including steady, but intermittent) basis.
It is economically practical to construct pumps in accordance with this invention for single use (disposable) applications. While medical applications are emphasized in this disclosure, the avoidance of contamination is desirable in other commercial or laboratory settings, and pumps constructed in harmony with the teachings of this disclosure are suitable for many such applications. It is generally advantageous for these pumps to be capable of rapid priming. The pump may thus be provided as an assembly, structured and arranged to hold the pressure rollers substantially out of contact with the flexible tubing comprising the pump chamber until deliberate force is applied to move those components into normal pumping association. The original such assembled condition permits unimpeded fluid flow through the tube, thereby enabling almost instantaneous priming of the pump. The second condition places the pump in pumping mode. Moving the rollers into the second assembled condition may be regarded as the final step in assembling the pump, and may be deferred until the pump is put into service.
The improvement of this invention may thus be regarded as a new arrangement of components for a peristaltic pump system in which rotating pressure elements are driven by a reduction system and are structured and arranged to revolve through a chamber in contact with a flexible tube. According to this invention, the pressure elements are incorporated into the reduction system. The pressure elements will usually comprise rotating pressure rollers driven by a gear reduction system. The pressure rollers are structured and arranged to revolve through a chamber with the outer surfaces of the rollers constituting pressure surfaces in contact with a flexible tube adjacent a reaction surface. Travel of the rollers causes positive displacement pumping action through the tube. The rollers are preferably mounted in roller assemblies in association with follower gears. The follower gears may be arranged to receive rotational force from a drive gear, which in turn receives power through a driven shaft element.
The pump system may include a first assembly comprising the driven shaft element; a second assembly comprising the pressure rollers; and a coupling mechanism associated with the reduction system constructed and arranged to transfer power from the driven shaft element to the pressure elements. The second assembly desirably includes a pair of structural members, the first of which includes a reaction surface. The flexible tube pumping chamber may then be mounted adjacent this reaction surface. The second structural member may carries the pressure rollers. Connection means associated with the first and second structural members are constructed and arranged to provide a first, priming, position of the rollers with respect to the reaction surface and a second, pumping, position of the rollers with respect to the reaction surface.
Ideally, the reaction surface is formed as a generally conical segment with a cone axis congruent with the axis of the driven shaft, and the rollers include generally frusto conical segments, and are mounted to turn on respective roller axes, each of which is approximately parallel the cone axis. The connection means may then be operable to adjust the spacing between the reaction surface and the pressure surfaces of the rollers such that the spacing (which captures the flexible tube) is relatively larger in the priming position and relatively smaller in the pumping position. A preferred arrangement of the connection means positions the first and second structural members in the priming position by holding the rollers in a first axial location with respect to the reaction surface. The connection means further accommodates relative axial movement of the first and second structural members into the pumping position, thereby moving the rollers into a second axial location with respect to the reaction surface. The first structural member may comprise a cassette body element and the second structural member may comprises a portion of a cassette housing. The first and second structural members may then be cooperatively adapted to couple together temporarily into the priming position during an assembly operation, and to be pressed permanently into the pumping position following priming of the flexible tube. This second positioning (into the pumping position) is conveniently accomplished in the field, such as in a clinical setting.
A typical dosage rate for pump assemblies applied to medical applications is less than about 50 xcexcl (micro liters) per pump rotor revolution, and such pumps are ordinarily operated to deliver outputs of less than about 100 ml (milliliters) per hour. A typical pump speed for such applications is about 60 rpm (revolutions per minute), with 600 rpm being about the maximum practical speed for pump assemblies of this scale. Of course, these scale and operating parameters are not critical to the operability of the pump assembly. More significantly, it is practical to construct assemblies within these parameters, in accordance with this invention, at low cost and within a relatively small volume, or envelope.
The pumps of this invention generally operate at a constant speed when in the xe2x80x9conxe2x80x9d condition. Throughput is thus controlled as a function of xe2x80x9conxe2x80x9d/xe2x80x9coffxe2x80x9d pulsed operation. Pulses are relied upon to distribute a specified dose over a prescribed time; typically a 24-hour period. Certain preferred embodiments of this invention incorporate an optical sensing arrangement constructed and arranged to count the number of rotations of the rotor arms during each pulse of operation. The data accumulated in this fashion can be processed, electronically or otherwise, to maintain a precisely controlled fluid delivery rate through the pump. An electronic control system associated with the drive motor for the pump may be programmed in conventional fashion to maintain a prescribed steady or variable delivery rate as desired.